Monomethyl esters of aliphatic phosphonic acids



United States Patent F MONOMETHYL ESTERS OF ALIPHATIC PHOSPHONIC ACIDS Herman E. Ries, .Ir., Chicago, Ill., assignor to Standard Oil Company, Chicago, 111., a corporation of Indiana No Drawing. Application February 17, 1955, Serial No. 488,983

Claims. (Cl. 260-461) This invention relates to new compositions of matter which are monomethyl esters of long chain hydrocarbon phosphonic acids.

Although a number of organic phosphonic acids and certain of their dialkyl esters have been recommended for use as lubricating oil additives and detergents, the corresponding monoalkane phosphonic acid esters, so far as I know, have not been made. This may be because of problem in the selective preparation of the monoesters, or more likely because of the poor probability, based upon experience with the known derivatives, that the mono-esters would possess any distinctively useful property. I have discovered however that a monomethyl ester of a long chain hydrocarbon phosphonic acid such as octadecane phosphonic acid possesses unusual anti-rust properties. This is surprising because film balance studies have shown that the free acid is a stronger film former than the monomethyl ester. For example, the collapse pressure, measured in dynes per centimeter by the Langmuir-Adam-Harkins film balance, of a film of the monomethyl ester of octadecane phosphonic acid is 48 compared to 53 for the free acid. On this basis, the free acid would be expected to show superiority in rust protection. In terms of practical utility, however, the monomethyl ester when tested for anti-rust properties under the conditions of the tilm-tenacity procedure of the ASTM D665 rust test was found to give perfect protection at a concentration as low as 0.001 percent where the free acid showed some rusting.- Moreover, the monomethyl ester shows a markedly different order of solubility in hydrocarbon fractions compared to the nearly insoluble free acid, thus promoting its use as a fuel or lubricant additive. The monomethyl esters are distinguished from higher monoalkyl esters in that alkyl groups larger than methyl appear to interfere with the close molecular packing associated with best film formation.

The monomethyl ester of octadecane phosphonic acid is an example of the compositions of the invention which comprise the monomethyl esters of phosphonic acids containing 21 long chain group comprising an essentially straight aliphatic chain of at least carbon atoms. Experimental studies of film forming properties have shown that a chain of at least this length in association with a strong polar group is necessary for close packing of the molecules in the form of a tenacious film. As the chain becomes longer the packing property improves, as does oil solubility. The chains may contain some branching and ring substitution without interfering with close packing. Alkyl benzene phosphonic acids however should be para-positioned to preserve the essentially straight chain character. The methyl branching of olefin chain polymers, such as propylene tetramer, or in polybutene chains, also appears unobjectionable.

The significant structural property of the new compounds centers about the phosphonic group which con- 2,7342% Patented Mar. 5,

tains a free acid group in addition to the monomethyl ester grouping as shown in the following formula:

OH Of the useful compositions, the longer chain compounds are most valuable, particularly octadecane phosphonic acid, although groups at least as long as 36 carbon atoms such as may be derived from hexatriacontanoic acid appear to be useful. In terms of practical availability however the C10 to C18 range including dodecane phosphonic and hexadecane phosphonic acids has special value.

The new compositions are useful as anti-rust agents in lubricating oils, turbine oils, gear oils and the like. They also have particular value for use in distillate fuels such as gasoline where they function not only as anti-rust agents but, as deposit modifiers, act to prolong spark plug life, to resist octane requirement increase of the engine with use and to eliminate pre-ignition. The concentration of use is about 0.00001 to 0.l percent by Weight in gasoline and about 0.0001 to about 1.0 percent in lubricating oils. The compounds also may be useful in other applications where strong film forming and/or surface active properties are important, e. g. detergents and insecticides.

The new compositions may be prepared in general by partial hydrolysis of the dimethyl esters of the corresponding long chain phosphonic acids or by reaction of mixed esters, such as the mixed methyl and t-butyl or benzyl esters, of the corresponding alkane phosphonic acid under conditions cracking or splitting off the t-butyl or benzyl group. The monomethyl ester of octadecane phosphonic acid, for example, also can be produced by direct partial esterification of the free acid with methanol. The monomethyl ester crystallizes from solution and dimethyl ester formed is separated as a liquid product.

Dimethyl esters of long chain phosphonic acids corresponding to the desired monomethyl ester can be pre pared in several ways. Dimethyl phosphite can be reacted with a long chain alkyl halide, e. g. octadecyl bromide, in the presence of metallic sodium. The resulting dimethyl ester then after recovery by distillation can be partially hydrolyzed with hydrochloric acid to obtain the monomethyl ester. Alternatively, the long chain halide, e. g. octadecyl bromide, can be reacted with a trimethyl phosphite at about to C. The dimethyl ester of the long chain phosphonic acid is formed and the methyl halide may be distilled off permitting the reaction to go to completion. In another method, the long chain olefin, e. g. octadecene-l, may be reacted with dimethyl phosphite in the presence of a peroxide catalyst or other free radical initiator such as a hypochlorite, or under the influence of ultraviolet light, at about 200 to 300 C. to obtain the dimethyl ester.

Example I n-Octadecane phosphonic acid, 10.33 grams (0.03 mole), was added to phosphorus pentachloride, 6.46 grams (0.03 mole), and reaction was initiated by warming the flask. When a homogeneous solution was obtained, a solution of methanol, 20 grams (0.62 mole), in pyridine, 23.7 (0.30 mole), was added dropwise. The reaction flask was surrounded by water to control the temperature. A solid appeared and remained throughout the reaction. After all of the methanol-pyridine solution was added, stirring was continued for an additional 15 minutes. To the reaction mixture was added 50 ml. of water and the contents of the flask were stirred vigorously. This caused an emulsion to form. n-Octanol was found to extract the organic material out of the emulsion. The octanol layer was separated and washed with water. Ethyl-acetate,.300 .ml., was added-tovtheoctanol" solution and a white solid precipitated (I). Acetone was period of :f'contact, 110 .ml. of

added to the filtrate and this solution allowed to stand A second solid (II) pre- (II) was recrysin the cold room overnight. cipitated which weighed 2.10igrams.

tallized iwicerfrom acetoneato give lA'l. gramsaofi white.. solid, 655-665". C: r This materialwasfoundto monomethyl; esterofoctadecane phosphonic. acidstoa regular grade gasoline in a concentration .of 5 poundsaof additive per. 1,000'barrels'of product. The gasoline also..-

contained? pounds per 1,000 barrels of..a commercial. anti-oxidant of the phenylene; diamine type and 9 pounds.v per 1,000 barrels of acommercial metal rdeactivator of thesalicyl aldehyde-diaminecondensation product type.- The composition .of the invention was tested'in a l6 hour..

rustv test. in comparison with the untreated gasoline and.. alsoin comparison with a gasolineblend containing: 10'- pounds per 1,000 barrels of acommercialanti-rust. addi-H' tive of the fattyacid type. The. rust test was conducted as follows: SAE-1020 steel panels [2 x 6 x 43" were belt. sanded clean of discoloration and pits. After cleaning with .hot naphtha followed .by hot acetone they were placed in 100ml. of the test fuel in a tall form 4 oz bottle. and. .allowed to stand forVz-.-hour. After this tapdvater. 'wasgaddedi and the capped bottle was rolled for 1 minute. The bottle was then stored in' an upright position. The appearance" of the strips was examined and evaluated after 16 hours exposure to the fuel layer and the Water layer.

Under the test conditions, the untreated gasoline control showed percent rusting of the test panel exposed to gasoline and percent-rustingof the panel exposed to water. The composition of the invention reduced rust sformation in gasoline toslO specks (where a speck is de fined as less than "one-millimeterindiameter) and the rustingin.svatenwasreduced to 50 percent. composition containing the commercial anti-rust showed 15 spots (where a spot is defined as an area of l to 3 mm.

,, in diameterfi'in-gasoli-ne-and percent rusting in water.

I claim:

l. A monomethyl esterof a phosphonic acid containing a long chain hydrocarbon group which contains an aliphatic chain of at least 10 to about 36 carbon atoms a in length. 1.

Lilhemonomethyl ester. of dodecane phosphonic acid",

3. The monomethyl ester of hexadecane phosphonic} acid.

4. rraa .monomethyl estenof octadecane phosphonic.

5.;A monomethyl ester of an alkane phosphonic acid.

whichcontainsabout .10 to .18 carbon atoms in the alkane group.

Refei'ences'Citd in the file'of this patent UNITED STATES. PATENTS 2,254,124? Stevens et al. Aug. 26,'l194l 2,587,340 Lewis et a1. Feb. 26', 1952- 2,594',454 i Kosola'poft Apr. 29,-1952 The gasoline 

1. A MONOMETHYL ESTER OF A PHOSPHONIC ACID CONTAINING A LONG CHAIN HYDROCARBON GROUP WHICH CONTAINS AN ALIPHATIC CHAIN OF AT LEAST 10 TO ABOUT 36 CARBON ATOMS IN LENGTH. 